The present invention relates to liquid material dispensing systems, and more particularly to apparatus and methods for dispensing multiple streams of liquid material to a substrate.
Liquid material dispensing systems are known in the art and generally comprise a liquid dispensing applicator having one or more dies configured to dispense the liquid material as filaments, ribbons, or other shapes. Applicators are available in many different configurations and are generally constructed to dispense liquid material in a specific form. For example, applicators for dispensing liquid material as filaments may have dies which include multiple liquid discharge outlets, or they may have multiple dies, each having a single liquid discharge outlet. In each configuration, however, the liquid material dispensed from each discharge outlet of a die is controlled by a single pressure source.
Often it is desired to apply liquid material to a substrate in the form of multiple filaments. For example, the coating of multiple strands of elastic substrate material, such as Lycra(copyright), for the manufacture of elasticized products can require individual filaments of liquid material to be dispensed onto each strand of the substrate. Because the elastic strands are typically arranged close to one another, usually spaced only a few millimeters apart, the coating of such strands is suited to liquid dispensing systems utilizing dies having multiple liquid outlets which are spaced apart a distance that corresponds to the spacing of the elastic strands. Accordingly, the coating of multiple strands of substrate material is typically accomplished by utilizing systems having dies with multiple liquid discharge outlets that are fed from a common source of pressurized liquid. One example of this type of die is described in U.S. Pat. No. 6,435,425, assigned to the assignee of the present invention.
One drawback of utilizing dies with multiple liquid discharge outlets to coat closely spaced strands of substrate material is that the multiple liquid discharge outlets are coupled to a common pressure source for dispensing the liquid material through the multiple outlets. Accordingly, in low flow-rate applications, the restriction of flow at one or more of the outlets is accommodated by increased flow at the remaining outlets of the die. This restriction in flow may be due to variation of local temperatures within the die that cause increased viscosity of the liquid material, contaminants in the liquid material, or a thick slug of liquid material moving through the die and restricting one or more of the outlets. Because the restriction in flow is accommodated by other outlets of the die, the dispense rate may not be equal across all outlets, causing uneven coating of the individual strands of substrate material. In the worst case, one or more outlets may become completely clogged while flow is accommodated by the other outlets. The result is a substrate material having an excessively heavy coating on some strands and no coating on other strands. To exacerbate the problem, conventional multi-outlet dies do not facilitate unclogging the blocked outlet, whereby the problem will continue until the dispensing system is shut down and fixed manually.
There is thus a need for an adhesive dispensing system utilizing dies with multiple liquid discharge outlets which overcomes drawbacks of the prior art, such as those described above.
The present invention provides a liquid dispensing system for dispensing liquid material from a plurality of liquid discharge outlets in a closely spaced arrangement and wherein the dispense rate from each of the liquid discharge outlets is independent of flow of liquid material from the other outlets. In one aspect of the invention, each liquid discharge outlet is in fluid communication with a flow-metering device, which controls the flow of liquid material from the outlet. This arrangement is particularly suited for low flow dispense rates and ensures that any restriction of flow through one liquid discharge outlet does not affect the flow of liquid from the remaining liquid discharge outlets. Furthermore, the system facilitates unclogging blocked liquid discharge outlets in that the restriction of flow through a blocked outlet increases pressure with respect to that outlet to thereby aid in the removal of the blockage.
In another aspect, the liquid dispensing system includes an adapter coupled between a die tip and a plurality of liquid dispensing modules. The adapter is configured to direct liquid material from each liquid dispensing module to respective liquid discharge passages on the die tip. Accordingly, the adapter permits the use of a die tip having liquid discharge passages which are spaced apart to correspond to the spacing of strands of substrate material to be used with dispensing modules on an applicator which are coupled to discrete flow-metering devices.
In yet another aspect of the present invention, a method of dispensing liquid material to a substrate includes supplying the liquid material to an applicator with at least one die having a plurality of liquid discharge outlets, independently controlling the flow of the liquid material to each of the discharge outlets and forcing the liquid material through each of the discharge outlets.
The features and objectives of the present invention will become more readily apparent from the following Detailed Description taken in conjunction with the accompanying drawings.